Untersuchungen über den Verlust von R-Plasmiden bei E. coli und Klebsiella pneumoniae im Verlauf von Bouillonpassagen

Plasmid RP1 (= Carb^rNeo^rKana^rTetra^rAmp^r) or Plasmid R100 (= Tetra^rStrept^rSulf^r) were transferred on 5 different strains of E. coli and on 3 strains of Kl. pneumoniae. Plasmid RK1 ( = Carb^rTet^rStrept^rAmp^r) was transferred on 3 strains of Kl. pneumoniae also. The resulting strains were cultured in 7 passages of Standard-I-Nutrient-Broth (Merck) and Mueller-Hinton-Broth (Becton-Dickinson); 48 colonies were examined for resistance to antibiotics of the different R-Plasmids.

In E. coli and in Kl. pneumoniae with R-Plasmids RP1 and RK1 no more than 2 colonies without one of several antibiotic resistances after 7 nutrient broth passages were seen. Striking loss of R-Plasmids was seen in Kl. pneumoniae with R-Plasmid R100 after the third passage. The behaviour of strains in Standard-I-Nutrient-Broth and Mueller-Hinton-Broth was not different.

In conclusion for sensitivity test colonies should be taken only from primary cultures. Furthermore it is recommended to pick up several colonies from one isolated strain for sensitivity test.